Chirped current profile with undershoot feature

ABSTRACT

Systems and methods for a providing a chirped current profile with an undershoot for a channel preamplifier are described. A method for writing bits in a magnetic recording disc may include applying an overshoot to a write current which is supplied to a magnetic writer of the magnetic recording disc and applying an undershoot to the write current after the overshoot is applied to at least partially de-saturate the magnetic writer. The method may also include writing a bit to the magnetic recording disc with the magnetic writer using the supplied write current. In some examples, the application of a short negative pulse after an overshoot portion of the write current waveform is delivered to the head during a write operation that writes the bit to the magnetic recording disc.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/242,382, filed on Aug. 19, 2016, abandoned, thedisclosure of which is incorporated in its entirety by this reference.

SUMMARY

The present disclosure is directed to methods and systems for relaxing apole in a magnetic write head during an active recording of a bit to amagnetic storage device. In some embodiments, the present systems andmethods may improve drive performance by reducing the time required forthe pole to relax after the initial transition of the bit written to themagnetic storage device. The present systems and methods may improveefficiency and user experience of a magnetic storage device.

A method for writing bits in a magnetic recording disc is described. Inone embodiment, the method may include applying an overshoot to a writecurrent which is supplied to a magnetic writer of the magnetic recordingdisc and applying an undershoot to the write current after the overshootis applied to at least partially de-saturate the magnetic writer. Themethod may also include writing a bit to the magnetic recording discwith the magnetic writer using the supplied write current.

Applying the undershoot may further include applying a short,opposite-polarity pulse of current from the current polarity to theexisting write current waveform (referred to herein as “write current”)during a write operation that writes the bit to the magnetic recordingdisc.

The method may also include determining an undershoot current level forthe undershoot based at least in part on an overshoot current level ofthe overshoot, wherein applying the undershoot further includes applyingthe undershoot current level to the magnetic writer.

In some examples, the method may include determining a write width for aprevious bit written to the magnetic recording disc. The method mayfurther include adjusting an undershoot current level for the undershootbased at least in part on the write width. The method may includedetermining a bit length of the bit to be written to the magneticrecording disc. In some examples, applying the undershoot to the writecurrent may further include applying the undershoot when the bit lengthis equal to or above a threshold bit length. The method may also includetruncating a time the undershoot is applied to the write current whenthe duration of the undershoot plus the delay before the undershoot isapplied is greater than a bit cell time.

Examples of the method may include determining at least one of amagnitude, duration, and delay of the undershoot, wherein applying theundershoot further includes applying the undershoot with at least one ofthe determined magnitude of the undershoot, a duration of theundershoot, and a delay before the undershoot is applied. In someexamples, applying the undershoot further includes applying a shift inone or more current pulses in the write current to produce anasymmetrical undershoot. The current value of the undershoot may be oneof greater than or equal to a current steady-state value and less thanor equal to a current steady-state value. The method may further includereturning the write current to a steady state value before a next datatransition.

In some examples, applying the undershoot to the write current mayfurther include waiting for a delay period to expire after the overshootis applied and applying the undershoot to the write current after adelay period has expired. The method may also include determining aduration of the undershoot, wherein applying the undershoot furtherincludes applying the undershoot for the determined duration. Otherexamples of the method may include receiving an external signal thatsignals a timing, magnitude, and duration for the undershoot andapplying the undershoot to the write current according to the externalsignal.

A device is also described. The device may include a preamplifier tosupply a write current to a magnetic writer of a storage device and awrite current device coupled between the preamplifier and the magneticwriter. In some examples, the write current device is configured toapply an overshoot to a write current which is supplied to the magneticwriter and apply an undershoot to the write current after the overshootis applied to at least partially de-saturate the magnetic writer,wherein the magnetic writer writes a bit to the storage device using themodified write current.

A storage system apparatus is also described. The storage systemapparatus may include a storage device having a magnetic write head anda preamplifier to supply a write current to the magnetic write head. Thestorage system apparatus may also include a write current device coupledbetween the preamplifier and the storage device, wherein the writecurrent device modifies the write current supplied to the magnetic writehead by applying an overshoot to the write current and applying anundershoot to the write current after the overshoot is applied to atleast partially de-saturate the magnetic write head, wherein themagnetic write head writes a bit to the storage device using themodified write current. In some examples, the write current deviceincludes a system-on-a-chip (SOC).

A storage system device is further described. The storage system devicemay include a preamplifier to supply a write current to a magneticwriter of a storage device, wherein the preamplifier comprises a circuitthat modifies the write current to include an undershoot after anovershoot is applied, wherein the undershoot at least partiallyde-saturates the magnetic writer during writing of a bit to the storagedevice. The circuit may further include a first resistor in series witha second resistor, wherein there is a first impedance mismatch betweenthe first resistor and the second resistor. The circuit may also includea third resistor in series with a fourth resistor, the third and fourthresistors being in parallel with the first and second resistors, whereinthere is a second impedance mismatch between the third resistor and thefourth resistor.

The foregoing has outlined rather broadly the features and technicaladvantages of examples according to this disclosure so that thefollowing detailed description may be better understood. Additionalfeatures and advantages will be described below. The conception andspecific examples disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present disclosure. Such equivalent constructions do notdepart from the scope of the appended claims. Characteristics of theconcepts disclosed herein—including their organization and method ofoperation—together with associated advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. Each of the figures is provided for the purpose ofillustration and description only, and not as a definition of the limitsof the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentdisclosure may be realized by reference to the following figures. In theappended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following a first reference label with a dash and asecond label that may distinguish among the similar components. However,features discussed for various components—including those having a dashand a second reference label—may apply to other similar components. Ifonly the first reference label is used in the specification, thedescription is applicable to any one of the similar components havingthe same first reference label irrespective of the second referencelabel.

FIG. 1 shows a block diagram of an example apparatus in accordance withvarious aspects of this disclosure;

FIGS. 2A and 2B show graphs of examples of write currents that may besupplied to a magnetic write head according to aspects of thedisclosure;

FIGS. 3A-3B show conceptual diagrams of write widths and correspondingwrite head currents;

FIG. 4 shows a graph of other examples of a write current that may besupplied to a magnetic write head and signals;

FIGS. 5A-5B show block diagrams of example input and output signals fora preamplifier.

FIG. 6 shows a circuit diagram of an example circuit that may beincluded in a preamplifier in accordance with various aspects of thisdisclosure;

FIG. 7 shows a block diagram of one or more example modules inaccordance with various aspects of this disclosure; and

FIGS. 8A-8B are flow charts illustrating an example of a method inaccordance with various aspects of this disclosure.

DETAILED DESCRIPTION

The following relates generally to the use of an undershoot in a writecurrent to at least partially relax a pole of a magnetic write head,particularly during an active recording of a bit to a magnetic recordingdisc. A magnetic recording disc is a storage device that uses magnetizedmedium to digitally store data. Magnetic recording discs are a form ofnon-volatile memory. Information is written to a magnetic recording discusing one or more magnetic write heads (referred to generally herein as“write heads”). Information is read from a magnetic recording disc usingone or more magnetic read heads.

A write head may write bits (e.g., a series of just 1s or just 0s) tothe magnetic recording disc. A length of a bit may be determined basedon how many 1s or 0s is in the bit. For a bit to be written, each of oneor more magnetic poles of the write head may be in one of two stateswhich correspond to opposite magnetic poles. When the magnetic recordingdisc is switching from writing a bit of one type to writing a bit of theother type (e.g., from writing 1s to writing 0s), the magnetic poles ofthe write head must at least partially flip magnetization. In otherwords, every time the data to be written switches from 1 to 0 orvice-versa, the magnetization of the write poles must reverse to theopposite magnetization. This transition to the opposite magnetizationmay take a substantial amount of time. Techniques described hereinreduce that time by partially demagnetizing the magnetic poles beforethe bit is completely written. This reduced transition time improves theefficiency and speed of the magnetic recording disc, which in turnimproves user experience.

One performance metric often used to characterize write heads is thetime it takes for a write pole reversal. However, there are slowerparameters which can be improved by using the chirped undershoot. Forexample, the processes related to domain wall motion andre-magnetization in side shields may become faster. Without theundershoot, these processes may occur on a nanosecond basis. During along bit (e.g., writing many 1s or 0s), the write head may becomesubstantially more saturated away from a tip of the pole, which wouldrequire larger current picks to ensure comparable risetime for the nextbit. Previous solutions include increasing the overshoot after long bitsor using pre-compensation to shift the time at which the current isbeing switched. Instead, the undershoot proposed herein reduces thesaturation away from the pole tip during a bit write.

Additionally, as the write pole saturates, simply reducing the currentdoes not result in a linear reduction in magnetic field. That is, thewrite pole is a non-linear system with significant dynamic hysteresiseffect. This may be due to factors including shape anisotropy and thefact that magnetization dynamics may possibly follow exponential timedependence. Shape anisotropy may cause the write head pole tip to besomewhat aligned along a direction perpendicular to an air-bearingsurface (ABS) of the magnetic recording disc, therefore helping tosupport significant magnetization of the pole tip unless torque(non-equilibrium magnetic field) is applied. A time constant of themagnetization dynamics may be inversely proportional to the torquepresent in the system. For example, a reduction of current by 10milliamperes (mA) at first may exert only minor torque back in thepaddle, underneath the coils, at the state which could reach substantiallevels of saturation even during the overshoot portion of the currentwaveform. This can considerably effect the pole tip only after asubstantial delay. These effects can become problematic as the writewidth is reduced in conventional systems. The techniques describedherein may ensure that the transition to smaller write widths occurswithin a short enough timeframe that the magnetization does not remaindominant for longer bits.

Overshooting the current level beyond a final steady state value maygenerate additional magnetic torque needed to achieve magnetizationchange within a limited timeframe. An undershoot (a “chirp” pulse) maybe applied after the overshoot in order to de-saturate the write head.As used herein, an undershoot may be a decrease in coil current to lowerlevels than previous, such as the steady state value. In some examples,an undershoot may even acquire an opposite current value with respect toboth the overshoot and steady state current amplitude.

Techniques described herein provide a time dependent current waveformwith an undershoot section following an overshoot section. Theundershoot section may be modifiable in amplitude, duration, and timing.A purpose of this “chirped” current profile (e.g., having theundershoot) may be to substantially speed up magnetic desaturation ofthe write head. This may result in the magnetic saturation of the writehead being almost directly determined by the steady state currentamplitude for long bits. In some examples, the steady state currentamplitude may be substantially below a saturation knee amplitude.

Techniques described herein provide methods, devices, and systems thatdecrease the write widths of long bits with limited degradation of thetransition quality. The methods, devices, and systems also may improvethe risetime and risetime delay, especially after long bits. Side trackerasure may also be improved and dynamic saturation of the trailingshield is provided. Because the write widths can be reduced using theundershoot feature, the track density of the magnetic recording disc maybe improved.

FIG. 1 shows a block diagram 100 of an apparatus 103 for use inelectronic communication, in accordance with various aspects of thisdisclosure. The apparatus 103 may include a drive controller 150, adrive buffer 125, a host interface logic 170, a channel 135, apreamplifier 120, a device 105, and a drive media 130. Each of thesecomponents may be in communication with each other and/or othercomponents directly and/or indirectly.

Using a current source, the preamplifier 120 may supply one or morewrite heads 115 of the drive media 130 with a write current. The device105 may cause the preamplifier 120 to apply an undershoot to the writecurrent, after an overshoot has been applied to the write current, inorder to at least partially de-saturate the write head 115.

The drive media 130 may also be referred to herein as a storage device.The drive media 130 may include one or more magnetic recording discs.The drive media 130 may include any combination of hard disc drives,solid state drives, and hybrid drives, or combinations thereof, thatinclude both hard disc and solid state drives. In some embodiments, thesystems and methods described herein may be performed on a singlemagnetic recording disc storage device. The techniques described hereinmay also apply to different recording and storing strategies, such as,for example, shingled magnetic recording (SMR), heat-assisted magneticrecording (HAMR), multi-sensor magnetic recording (MSMR), and the like.In some cases, the techniques described herein may be performed onmultiple storage devices or a network of storage devices. Examples ofthe drive media 130 may include a storage server, a storage enclosure, astorage controller, storage drives in a distributed storage system,storage drives on a cloud storage system, storage devices on personalcomputing devices, storage devices on a server, or any combinationthereof.

In some configurations, the device 105 may include a write currentcomponent 140. In one example, the device 105 may be coupled to thepreamplifier 120. In other examples, the device 105 may be part of thepreamplifier 120. In some embodiments, the device 105, the preamplifier120, and the drive media 130 may be components of a magnetic recordingdisc. Alternatively, the device 105 and the preamplifier 120 may be acomponent of a host (e.g., operating system, host hardware system, etc.)of the drive media 130.

In other examples besides the one shown in FIG. 1, the device 105 may bea computing device with one or more processors, memory, and/or one ormore storage devices. In some cases, the device 105 may include awireless storage device. In some embodiments, the device 105 may includea cloud drive for a home or office setting. In one embodiment, thedevice 105 may include a network device such as a switch, router, accesspoint, or any combination thereof. In one example, the device 105 may beoperable to receive data streams, store and/or process data, and/ortransmit data from, to, or in conjunction with one or more local and/orremote computing devices.

The device 105 may include a database. In some cases, the database maybe internal to the device 105. For example, a storage device, such asthe drive media 130, may store a database. Additionally, oralternatively, the database may include a connection to a wired and/or awireless database. Additionally, as described in further detail herein,software and/or firmware (e.g., stored in memory) may be executed on aprocessor of the device 105. Such software and/or firmware executed onthe processor may be operable to cause the device 105 to monitor,process, summarize, present, and/or send a signal associated with theoperations described herein.

Some examples include an external component 180 coupled to thepreamplifier 120. In some examples, the external component 180 iscoupled to the device 105. The external component 180 may connect toeither of these components via a wired or wireless connection. Theexternal component 180 may provide an external signal to the device 105or the preamplifier 120. Such an external signal may modify theundershoot applied to the write current.

In one embodiment, the drive media 130 may be internal to the device105. As one example, the device 105 may include a storage controllerthat interfaces with storage media of the drive media 130.

One or more of the components of the apparatus 103, individually orcollectively, may be implemented using one or more application-specificintegrated circuits (ASICs) adapted to perform some or all of theapplicable functions in hardware. Alternatively, the functions may beperformed by one or more other processing units (or cores), on one ormore integrated circuits. In other examples, other types of integratedcircuits may be used (e.g., Structured/Platform ASICs, FieldProgrammable Gate Arrays (FPGAs), and other Semi-Custom ICs), which maybe programmed in any manner known in the art. The functions of eachcomponent may also be implemented—in whole or in part—with instructionsembodied in memory formatted to be executed by one or more generaland/or application-specific processors.

In one embodiment, the drive controller 150 may include a processor 155,a buffer manager 160, and a media controller 165. The drive controller150 may process, via the processor 155, read and write requests inconjunction with the host interface logic 170, which acts as aninterface between the apparatus 103 and a host of apparatus 103 (e.g.,an operating system, host hardware system, etc.). The drive buffer 125may hold data temporarily for internal operations of the apparatus 103.For example, a host may send data to the apparatus 103 with a request tostore the data on the drive media 130. The drive controller 150 mayprocess the request and, through the channel 135 and the preamplifier120, cause the drive media 130 to store the received data. In somecases, a portion of data stored in the drive media 130 may be copied tothe drive buffer 125 and the processor 155 may process or modify thiscopy of data and/or perform an operation in relation to this copy ofdata held temporarily in the drive buffer 125.

Although depicted outside of the drive controller 150, in someembodiments, the device 105 may include software, firmware, and/orhardware located within the drive controller 150. For example, thedevice 105 may include at least portions of the processor 155, thebuffer manager 160, and/or the media controller 165. In one example, thedevice 105 may include one or more instructions executed by theprocessor 155, the buffer manager 160, and/or the media controller 165.The device 105 may be configured to apply an undershoot to a writecurrent that the preamplifier 120 supplies to the drive media 130 duringa write operation. The device 105 may apply the undershoot during anactive bit write after an overshoot is applied to the write current. Thedevice 105 may modify the undershoot based on parameters determined fromcertain conditions or user programmable parameters.

FIG. 2A shows a graph 200 of an example of a write current 205 that maybe supplied to a magnetic write head. A preamplifier, such as thepreamplifier 120 of FIG. 1, may supply the write current 205 to a writehead, such as the write head 115 of FIG. 1. The graph 200 shows acurrent level 215 over time 220. The write current 205 includes anovershoot 230 and an undershoot 235. The undershoot 235 happens afterthe overshoot 230 is applied, during an active bit writing time 225. Acurrent value 210 is a steady-state current value, and saturation point220 is a current value corresponding to a maximum magnetic saturation ofthe one or more poles of the write head.

The undershoot 235 may be a decrease in the write current 205 due to adecrease in coil current to lower levels than the write current 205 waspreviously at. For example, the undershoot 235 may be due to a drop incurrent from the steady state value 210. The undershoot 235 may be ashort pulse of current to the write current 205 during a write operationthat writes a bit to a magnetic recording disc. In some examples, theundershoot 235 may be a short negative pulse of current. The undershoot235 may help to de-magnetize the poles of the magnetic read head. Afterthe undershoot 235 is applied, the write current 205 may be returned tothe steady-state value 210. The steady-state value 210 may be somewhatlower than a saturation knee in some examples.

The undershoot 235 may at least partially de-saturate the write headafter the overshoot is applied. The duration of the undershoot may bebased on one or more of several parameters. Such parameters may includea risetime, amplitude, and duration of the overshoot, and a selectedduration parameter. An example amplitude of the undershoot 235 may be inthe range of approximately −30 mA to 30 mA. In other designs, otheramplitudes are used for the undershoot 235. In one example, the durationof the undershoot may be approximately 100-100 picoseconds (ps). Othertime ranges for the duration may be used. For example, smaller valuesmay be used for designs that use narrower write widths.

The parameters of the undershoot and overshoot may be interconnectedwith one another. For example, increasing the overshoot amplitude maypotentially improve the transition time, however it may also requirechanging the undershoot amplitude. These parameters may be locallychosen for specific performance. One example conventional waveform mayhave a very fast (50 ps) overshoot risetime, a substantial overshootamplitude with a very fast overshoot duration, followed by quick decayof current amplitude towards the steady state values. This kind ofprofile does allow for some write width control, as it prevents writerfrom substantially saturating and therefore can be effective in writewidth reduction, especially with 1 turn designs with low recess of thecoil. However, due to the need to have fast overshoot, this design isassociated with very large erasure. An example waveform according to thetechniques described herein is shown in FIG. 2A. The write current 205has a substantial overshoot risetime (150 ps), which together with theovershoot duration roughly encompasses the entire length of 1 T bit,followed by undershoot to −20 mA. The write current 205 then returns tosteady state amplitude.

Effects of the current profile of the write current 205 may be asignificant reduction of write width and increase in track density. Insome examples, these benefits may come at the expense of some reductionof transition quality. The following effects interplay. Worse transitionsignal-to-noise ratio (SNR) due to transition between an unsaturatedstate (e.g., reduced field and write width) and saturated or unsaturatedstate rather than between two saturated states. However this effect maybe partially offset by better risetime and risetime delay.

As side shields are also unsaturated and undergo less extreme dynamicchanges, track erasure is improved. However, because the write width isreduced some substantial saturation of the write pole during theovershoot segment might result in worse erasure. Further, the amplitudeof the write field used to write long bits may be reduced proportionallywith the write width. This means that the DC erased signal to noiseratio (DCSNR) may be reduced. Some examples do not allow a reverseoverwrite to drop below the DCSNR level at which the previously writtenbit become a source of additional noise. Since at reduced saturation,approximately the same write width corresponds to larger set of states,write to write variations increase proportionally.

In some examples, even a very small reduction of the write field (forexample, to about 95% of the maximum amplitude) may improve thetransition quality because erasure and risetime benefits outweighinsignificant reduction in the magnetic field. However, a largerreduction may be used to achieve a desired analog to digital conversion(ADC). For example, a reduction leading to writing with 85% of thenominal write plus erase (WPE) may be used. Other reductions of thewrite field may be used in other examples.

FIG. 2B shows a graph 200-a of an example of a write current 205-a thatmay be supplied to a magnetic write head. A preamplifier, such as thepreamplifier 120 of FIG. 1, may supply the write current 205-a to awrite head, such as the write head 115 of FIG. 1. The graph 200-a showsa waveform of the write current 205-a over time 220-a. The write current205-a includes an overshoot 230-a and an undershoot 235-a. Theundershoot 235-a happens after the overshoot 230-a is applied, during anactive bit writing. A current value 210-a is a steady-state currentvalue.

The graph 200-a also illustrates a section 250 where prior bits werewritten to the storage media. The graph 200-a also shows a transition260 where the write current 205-a ramps up to write a bit to the storagemedia. Also illustrated are configurable aspects of the undershoot 235-aas described herein.

FIG. 3A illustrates a conceptual diagram 300 of write widths andcorresponding write head currents. FIG. 3A includes a write current210-b and shows the corresponding transitions on the drive media, suchas the drive media 130 of FIG. 1. A current portion 305 corresponds toan example 2 T bit time (down-track) and shows the length of 2 bits. Acurrent portion 310 corresponds to an example 1 T bit time (down-track)and shows the length of 1 bit.

FIG. 3B provides a conceptual image 350 of the write widths of thecurrent portions 305 and 310 of FIG. 3A. The portion 360 corresponds tothe 2T bit time of the current portion 305. The portion 365 correspondsto the 1T bit time of the current portion 310. Other examples arepossible and FIG. 3B is merely one description.

FIG. 4 shows a curve 400 of another example of a write current 205-athat may be supplied to a magnetic write head. The curve 400 shows awaveform for the write current 205-a of current over time, as similar tothe graph 200 of FIG. 2A. A preamplifier, such as the preamplifier 120of FIG. 1, may supply the write current 205-a to a write head, such asthe write head 115 of FIG. 1. Waveforms for example external signals 405(US_EXT_SIGNAL) and write data 415 are also shown.

The techniques described herein may introduce a wave-shaping controlvariable into the preamplifier write driver circuitry. Legacy featuresthat are user programmable include Iwss (Steady State), Iosa(Overshoot), Idur (Duration), and Itrise (Rise time). Programmablevariations of these features can be applied to all magnetic transitionsor just some of the transitions based on the bit length. Here, threeadditional user programmable control may be added to describe themagnitude, duration, and delay of the undershoot. These include Ius(e.g., a current level for the undershoot), Ius_dur (e.g., an undershootduration), and Ius_delay (e.g., an undershoot start delay). FIG. 4 showsthese controls and what features on the waveform they control.

An example approximate scale and magnitude of the control knobs ofprogrammable registers in a preamplifier is as follows. For Ius, themagnitude of the undershoot itself may have a range of approximately 0to 90 mA, for example. The pulse may produce an undershoot greater thanor equal to a maximum value of Iwss. An example maximum Iwss may bearound 60 mA. If the Ius is approximately 90 mA and Iwss isapproximately 60 mA, the result will be an undershoot that extends downfrom 60 mA to a minimum of −30 mA.

The placement of the undershoot can follow immediately after the mainovershoot pulse and the duration (Ius) has expired, or it can bedelayed. The parameter Ius_delay may be set to delay the placement ofthe undershoot. For example, if the IOSD is 0, the natural decay timemay be around 150 ps or it can be delayed in 20-50 ps increments fromthat point up to 1 ns or longer. For example if a Iosd duration isprogrammed by the user to be 600 ps and the Ius_delay is programmed tobe 1 ns, then the time at which the undershoot occurs relative to therising edge is 1.6 nS or 1 nS after the overshoot duration timer hasexpired.

The parameter Ius_dur controls the width of the chirped pulse itself andcan be programmable. For example, Ius_dur can be in approximately arange of 100 ps to 600 ps or more.

The parameters Ius_asymetry and Ius_asym_pol may apply a shift or offsetin the positive/negative pulses producing an asymmetric undershoot. Themagnitude of the offset may be either added or subtracted from bothpolarities and may be on the order of 15-30 mA. The polarity of theoffset can be selected via a Ius_asym_pol bit.

FIG. 4 illustrates three example cases relative to bit cell timing. Case1 is represented in FIG. 4 as portion 420 of the write current 205-a. Incase 1, the Ius_delay plus Idur is sufficiently less than the bit celltime, the full undershoot pulse is applied and the write current 205-awill fully return to the programmed Iwss value before proceeding to thenext data transition.

Case 2 is represented as portion 430 of the write current 205-a. Case 2occurs when only Ius_delay is less than the bit cell time but the sum ofIus_dur plus Ius_delay is greater than the bit cell time, the chirppulse is allowed to start but the duration of the pulse is truncated atthe next data transition and the polarity is allowed to reverse. Thisproduces a shelf like waveform prior to the next transition. The Idurtimer may be truncated at the data transition boundary and thetransition proceeds to the opposite polarity.

Case 3 is represented as portion 440 of the write current 205-a. IfIus_delay is larger than the entire bit cell time (in other words, adata transition is received before the Ius_delay timer has expired), theundershoot is not applied and all timers are reset for the nexttransition. If a string of transitions are all shorter than theIus_delay, then none of them will observe an undershoot.

In some examples, an external signal, such as US_EXT_SIGNAL 405, may beprovided to the preamplifier to adjust the write current 205-a. Rises orfalls of the US_EXT_SIGNAL 405 may affect the write current 205-a.

The methods described above may be used with the general asymmetricwriting and uni-polar writing methods for the rest of the waveformfeatures (i.e., if the waveform or any part of the waveform is shifted,the Ius applies to relative to that shift). Additional asymmetry may beapplied directly via the Ius_asymmetry in addition to any otherasymmetric shifting of the rest of the signal (i.e., the Iwss can beasymmetrically shifted negative, while the Ius_asym can be shiftedpositive).

FIG. 5A shows a block diagram of example input and output signals for apreamplifier 120-b. The preamplifier 120-b may be an example of one ormore aspects of the preamplifier 120 of FIG. 1. An SOC channel 135-aprovides write data 505 to the preamplifier 120-b. The preamplifier120-b may supply the write current 205 to a write head 115-b. The SOCchannel 135-a may be an example of one or more aspects of the channel135 of FIG. 1. The write head 115-a may be an example of one or moreaspects of the write head 115 of FIG. 1. The preamplifier 120-b providesthe write data 505 and a write current 510 to the write head 115-a.

In some examples, no additional hardware lines from either the SOCchannel 135-a nor the preamplifier 120-b are needed to signal when theundershoot pulse should occur. This may keep complexity and die sizeminimal for both the SOC channel 135-a and the preamplifier 120-b.

FIG. 5B shows a block diagram of example input and output signals for apreamplifier 120-c. The preamplifier 120-c may be an example of one ormore aspects of the preamplifier 120 of FIGS. 1, 2, and 5B. An SOCchannel 135-b provides write data 505-a and an external signal 515 tothe preamplifier 120-b. The preamplifier 120-b may supply the writecurrent 510-a to a write head 115-b. The SOC channel 135-a may be anexample of one or more aspects of the channel 135 of FIG. 1 or 5A. Thewrite head 115-b may be an example of one or more aspects of the writehead 115 of FIG. 1 or 5A.

FIG. 6 shows a circuit diagram of an example circuit 600 that may beincluded in a preamplifier in accordance with various aspects of thisdisclosure. The circuit 600 may be a flex circuit located prior to ahead gimbal assembly (HGA) attach. The circuit 600 may exacerbate anopposing polarity undershoot immediately following the main overshoot.The circuit 600 may modify the write current to include an undershootafter an overshoot is applied, wherein the undershoot at least partiallyde-saturates the magnetic writer during writing of a bit to the storagedevice. The circuit 600 may be used instead of, or in addition to, themethods described above to apply the undershoot.

The circuit 600 includes an amplifier 605 coupled to an inductor 620.Two resistors 610 and 615 may be between the amplifier 605 and theinductor 620 on separate lines. The circuit 600 may include the firstresistor 610 in series with a second resistor 615, wherein there is afirst impedance mismatch between the first resistor 610 and the secondresistor 615. The circuit 600 may also include a third resistor 610-a inseries with a fourth resistor 615-a which are in parallel with the firstand second resistors 610 and 615, wherein there is a second impedancemismatch between the third resistor 610-a and the fourth resistor 615-a.In some examples, the resistors 610 and 610-a have a same impedance andthe resistors 615 have a same impedance different from that of theresistors 615-a. In some examples, the resistors 610 and 610-a are Z_Tgaresistors and the resistors 615 and 615-a are PCC resistors. The PCCresistors 615 and 615-a may have a much higher impedance than the Z_Tgaresistors 610 and 610-a.

By intentionally reducing the output impedance significantly, anundershoot can be realized immediately after the main overshoot pulse.In this scenario, the pulse duration is largely unchangeable unlessinterconnect impedance profiles are used to extend the duration via thetheory of multiple reflections. This method may reduce the depth of theundershoot. The magnitude of the undershoot may be directly related tothe amount of overshoot programmed and the steady state.

FIG. 7 shows a block diagram of one or more example modules of a writecurrent component 140-a in accordance with various aspects of thisdisclosure. The write current component 140-a may be an example of oneor more aspects of the write current component 140 of FIG. 1. The writecurrent component 140-a includes an undershoot module 705, an overshootmodule 710, an undershoot adjustment module 715, a bit write widthmodule 720, and an undershoot truncate module 725.

The overshoot module 705 applies an overshoot to a write current whichis supplied to a magnetic writer of a magnetic recording disc. In someexamples, the overshoot module 705 may return the write current to asteady state value before a next data transition.

The undershoot module 710 applies an undershoot to the write currentafter the overshoot is applied to at least partially de-saturate themagnetic writer. The undershoot module 710 may apply a short pulse ofcurrent to the write current during a write operation that writes thebit to the magnetic recording disc. In some examples, the undershootmodule 710 may apply the undershoot with the current level determined bythe undershoot adjustment module 715. In some examples, the undershootmodule 710 applies the undershoot to the write current after a delayperiod has expired. The application of the undershoot may be causal suchthat the write current component 140-a does not have to have a priorknowledge of the prior or upcoming bits.

The undershoot adjustment module 715 may determine an undershoot currentlevel for the undershoot based at least in part on an overshoot currentlevel of the overshoot. The undershoot adjustment module 715 may alsodetermine at least one of a magnitude, duration, and delay of theundershoot. Applying the undershoot may further include applying theundershoot with at least one of the determined magnitude of theundershoot, a duration of the undershoot, and a delay before theundershoot is applied. The undershoot module 710 may apply a shift inone or more current pulses in the write current to produce anasymmetrical undershoot. The undershoot adjustment module 715 maydetermine a duration of the undershoot and the undershoot module 710 mayapply the undershoot for the determined duration. In some examples, theundershoot adjustment module 715 receives an external signal thatsignals a timing, magnitude, and duration for the undershoot and appliesthe undershoot to the write current according to the external signal.

The bit write width module 720 may adjust a write width for the bit tobe written to the magnetic recording disc based on feedback from thewrite width of a previously written bit. The undershoot current levelmay be adjusted based at least in part on the previous bit's width. Thebit write width module 720 may also determine a bit length in time ofthe bit to be written to the magnetic recording disc. In some examples,applying the undershoot to the write current further includes applyingthe undershoot when the bit length is equal to or above a threshold bitlength. The threshold bit length may be a duration of the bit length intime.

The undershoot truncate module 725 may truncate a time the undershoot isapplied to the write current when the duration of the undershoot plusthe delay before the undershoot is applied is greater than a bit celltime.

FIG. 8A is a flow chart illustrating an example of a method 800 inaccordance with various aspects of this disclosure. One or more aspectsof the method 800 may be implemented in conjunction with the device 105of FIG. 1, the circuit 600 of FIG. 6, and/or the write current component140 depicted in FIGS. 1 and 7. In some examples, a backend server,computing device, and/or storage device may execute one or more sets ofcodes to control the functional elements of the backend server,computing device, and/or storage device to perform one or more of thefunctions described below. Additionally or alternatively, the backendserver, computing device, and/or storage device may perform one or moreof the functions described below using special-purpose hardware.

The method 800 begins at block 805 with writing one or more test datatransitions to the magnetic recording disc. The method 800 measures thewrite width (in tracks per inch, for example) and the on track bitdensity (BPI) of the test at block 810. At block 815, the method 800determines whether the TPI or the BPI could be improved by furthermodification of the undershoot. If so, the method proceeds to block 820,where the undershoot is adjusted in one of amplitude, width, or delay.If the TPI nor the BPI could be improved by further medication of theundershoot, the method 800 is done improvising the write process at thisstage, and the method 800 proceeds along path 825 to FIG. 8B.

FIG. 8B is another flow chart illustrating an example of a method 800-ain accordance with various aspects of this disclosure. The method 800-amay be combined with the method 800 of FIG. 8A. One or more aspects ofthe method 800-a may be implemented in conjunction with the device 105of FIG. 1, the circuit 600 of FIG. 6, and/or the write current component140 depicted in FIGS. 1 and 7. In some examples, a backend server,computing device, and/or storage device may execute one or more sets ofcodes to control the functional elements of the backend server,computing device, and/or storage device to perform one or more of thefunctions described below. Additionally or alternatively, the backendserver, computing device, and/or storage device may perform one or moreof the functions described below using special-purpose hardware.

FIG. 8B begins at path 825 from FIG. 8A and proceeds to block 830 withreceiving a write operation at a drive controller of a magneticrecording disc. The method 800-a further includes supplying writecurrent to the magnetic recording disc at block 835. Block 835 may beperformed by a preamplifier and/or device as described herein. The writehead may begin to write the bit at block 840.

At block 845, the method 800-a includes determining whether a magnitude,duration, or delay of the undershoot has been set. If not, the method800-a proceeds to block 850. If so, the method 800-a proceeds to block865.

At block 850, the undershoot is adjusted based on the set parameters. Atblock 855, the overshoot is applied. At block 860, the undershoot isapplied after application of the overshoot. The method 800-a thenproceeds to block 890, returning the current value to the write steadystate value.

Alternatively, at block 865, at least one of the magnitude, duration, ordelay for the undershoot has been set, so the method 800-a includesadjusting the undershoot based on the set parameters. At block 870, theovershoot is applied. At block 875, the undershoot is applied accordingto the set parameters, after the overshoot has been applied.

At block 880, the method 800-a determines if the bit write duration intime is greater than or equal to a threshold bit length in time. If so,the method 800-a truncates the undershoot at block 885. The method 800-athen returns the write current to the write steady state value at block890. At block 895, the method 800-a further includes finishing writingthe bit to the disc.

In some examples, aspects from the methods 800 and 800-a may be combinedand/or separated. It should be noted that the methods 800 and 800-a isjust an example implementation, and that the operations of the methods800 and 800-a may be rearranged or otherwise modified such that otherimplementations are possible.

The techniques described herein differ from other pattern dependentwrite methods that simply boost 1 T current to enhance write-ability byinstead attacking the de-magnetization/torque issue associated with longtransitions themselves rather than just adding more current to the shorttransitions without dealing with the long time constant it takes to pullthe head out of saturation from the prior bit. This may also enhance theSTE and ATI performance.

The detailed description set forth above in connection with the appendeddrawings describes examples and does not represent the only instancesthat may be implemented or that are within the scope of the claims. Theterms “example” and “exemplary,” when used in this description, mean“serving as an example, instance, or illustration,” and not “preferred”or “advantageous over other examples.” The detailed description includesspecific details for the purpose of providing an understanding of thedescribed techniques. These techniques, however, may be practicedwithout these specific details. In some instances, known structures andapparatuses are shown in block diagram form in order to avoid obscuringthe concepts of the described examples.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and components described in connectionwith this disclosure may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), an ASIC, anFPGA or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, or any combination thereof designedto perform the functions described herein. A general-purpose processormay be a microprocessor, but in the alternative, the processor may beany conventional processor, controller, microcontroller, and/or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor,multiple microprocessors, one or more microprocessors in conjunctionwith a DSP core, and/or any other such configuration.

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations.

As used herein, including in the claims, the term “and/or,” when used ina list of two or more items, means that any one of the listed items canbe employed by itself, or any combination of two or more of the listeditems can be employed. For example, if a composition is described ascontaining components A, B, and/or C, the composition can contain Aalone; B alone; C alone; A and B in combination; A and C in combination;B and C in combination; or A, B, and C in combination. Also, as usedherein, including in the claims, “or” as used in a list of items (forexample, a list of items prefaced by a phrase such as “at least one of”or “one or more of”) indicates a disjunctive list such that, forexample, a list of “at least one of A, B, or C” means A or B or C or ABor AC or BC or ABC (e.g., A and B and C).

In addition, any disclosure of components contained within othercomponents or separate from other components should be consideredexemplary because multiple other architectures may potentially beimplemented to achieve the same functionality, including incorporatingall, most, and/or some elements as part of one or more unitarystructures and/or separate structures.

Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation,computer-readable media can comprise RAM, ROM, EEPROM, flash memory,CD-ROM, DVD, and/or other optical disc storage, magnetic disc storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code means in the form of instructions ordata structures and that can be accessed by a general-purpose orspecial-purpose computer, and/or a general-purpose or special-purposeprocessor. Disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disc and Blu-ray discwhere discs usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above are also includedwithin the scope of computer-readable media.

The previous description of the disclosure is provided to enable aperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the scope of thedisclosure. Thus, the disclosure is not to be limited to the examplesand designs described herein but is to be accorded the broadest scopeconsistent with the principles and novel features disclosed.

This disclosure may specifically apply to security system applications.This disclosure may specifically apply to storage system applications.In some embodiments, the concepts, the technical descriptions, thefeatures, the methods, the ideas, and/or the descriptions mayspecifically apply to storage and/or data security system applications.Distinct advantages of such systems for these specific applications areapparent from this disclosure.

The process parameters, actions, and steps described and/or illustratedin this disclosure are given by way of example only and can be varied asdesired. For example, while the steps illustrated and/or described maybe shown or discussed in a particular order, these steps do notnecessarily need to be performed in the order illustrated or discussed.The various exemplary methods described and/or illustrated here may alsoomit one or more of the steps described or illustrated here or includeadditional steps in addition to those disclosed.

Furthermore, while various embodiments have been described and/orillustrated here in the context of fully functional computing systems,one or more of these exemplary embodiments may be distributed as aprogram product in a variety of forms, regardless of the particular typeof computer-readable media used to actually carry out the distribution.The embodiments disclosed herein may also be implemented using softwaremodules that perform certain tasks. These software modules may includescript, batch, and/or other executable files that may be stored on acomputer-readable storage medium or in a computing system. In someembodiments, these software modules may permit and/or instruct acomputing system to perform one or more of the exemplary embodimentsdisclosed here.

This description, for purposes of explanation, has been described withreference to specific embodiments. The illustrative discussions above,however, are not intended to be exhaustive or limit the present systemsand methods to the precise forms discussed. Many modifications andvariations are possible in view of the above teachings. The embodimentswere chosen and described in order to explain the principles of thepresent systems and methods and their practical applications, to enableothers skilled in the art to utilize the present systems, apparatus, andmethods and various embodiments with various modifications as may besuited to the particular use contemplated.

What is claimed is:
 1. A method for writing bits in a magnetic recordingdisc, comprising: applying an overshoot to a write current which issupplied to a magnetic writer of the magnetic recording disc; applyingan undershoot to the write current after the overshoot is applied to atleast partially de-saturate the magnetic writer; and writing a bit tothe magnetic recording disc with the magnetic writer using the suppliedwrite current, wherein applying the undershoot comprises applying ashort pulse of current to the write current during a write operationthat writes the bit to the magnetic recording disc.
 2. The method ofclaim 1, further comprising: determining an undershoot current level forthe undershoot based at least in part on an overshoot current level ofthe overshoot; and wherein applying the undershoot further comprisesapplying the undershoot current level to the magnetic writer.
 3. Themethod of claim 1, further comprising: determining a write width of aprevious bit written to the magnetic recording disc; and adjusting anundershoot current level for the undershoot based at least in part onthe write width.
 4. The method of claim 1, further comprising:determining a bit length in time of the bit to be written to themagnetic recording disc; and wherein applying the undershoot to thewrite current further comprises applying the undershoot when the bitlength is equal to or above a threshold bit length.
 5. The method ofclaim 1, further comprising: determining at least one of a magnitude,duration, and delay of the undershoot; wherein applying the undershootfurther comprises applying the undershoot with at least one of thedetermined magnitude of the undershoot, a duration of the undershoot,and a delay before the undershoot is applied.
 6. The method of claim 5,further comprising: truncating a time the undershoot is applied to thewrite current when the duration of the undershoot plus the delay beforethe undershoot is applied is greater than a bit cell time.
 7. The methodof claim 1, wherein applying the undershoot further comprises: applyinga shift in one or more current pulses in the write current to produce anasymmetrical undershoot.
 8. The method of claim 1, further comprising:returning the write current to a steady state value before a next datatransition.
 9. The method of claim 1, wherein a current value of theundershoot is one of greater than or equal to a current steady-statevalue and less than or equal to a current steady-state value.
 10. Themethod of claim 1, wherein applying the undershoot to the write currentfurther comprises: waiting for a delay period to expire after theovershoot is applied; and applying the undershoot to the write currentafter a delay period has expired.
 11. The method of claim 1, furthercomprising: determining a duration of the undershoot; and whereinapplying the undershoot further comprises applying the undershoot forthe determined duration.
 12. The method of claim 1, further comprising:receiving an external signal that signals a timing, magnitude, andduration for the undershoot; and applying the undershoot to the writecurrent according to the external signal.
 13. A device comprising: apreamplifier to supply a write current to a magnetic writer of a storagedevice; and a write current device coupled between the preamplifier andthe magnetic writer, wherein the write current device is configured to:apply an overshoot to a write current which is supplied to the magneticwriter; and apply an undershoot to the write current after the overshootis applied to at least partially de-saturate the magnetic writer,wherein the magnetic writer writes a bit to the storage device using themodified write current, and wherein applying the undershoot comprisesapplying a short pulse of current to the write current during a writeoperation that writes the bit to the magnetic recording disc.
 14. Thedevice of claim 13, wherein the write current device is furtherconfigured to determine an undershoot current level for the undershootbased at least in part on an overshoot current level of the overshoot,wherein applying the undershoot further comprises applying theundershoot current level to the magnetic writer.
 15. The device of claim13, wherein the write current device is further configured to determinea write width of a previous bit written to the magnetic recording discand adjust an undershoot current level for the undershoot based at leastin part on the write width.
 16. The device of claim 13, wherein thewrite current device is further configured to determine a bit length intime of the bit to be written to the magnetic recording disc, whereinapplying the undershoot to the write current further comprises applyingthe undershoot when the bit length is equal to or above a threshold bitlength.
 17. The device of claim 13, wherein the write current device isfurther configured to determine at least one of a magnitude, duration,and delay of the undershoot, wherein applying the undershoot furthercomprises applying the undershoot with at least one of the determinedmagnitude of the undershoot, a duration of the undershoot, and a delaybefore the undershoot is applied.
 18. A storage system apparatuscomprising: a storage device having a magnetic write head; apreamplifier to supply a write current to the magnetic write head; and awrite current device coupled between the preamplifier and the storagedevice, wherein the write current device modifies the write currentsupplied to the magnetic write head by applying an overshoot to thewrite current and applying an undershoot to the write current after theovershoot is applied to at least partially de-saturate the magneticwrite head, wherein the magnetic write head writes a bit to the storagedevice using the modified write current, and wherein applying theundershoot comprises applying a short pulse of current to the writecurrent during a write operation that writes the bit to the magneticrecording disc.